1. Field of the Invention
The present invention relates to a polyarylene sulfide (hereinafter "PAS") resin composition that is excellent in moldability and in mechanical properties. More specifically the present invention relates to a PAS resin composition characterized in that the separability of a molding from the metal mold (hereafter referred to as "mold separability") can be drastically improved independently of the mold temperature at the time of injection molding, thereby shortening the molding time and increasing mechanical strength of the molding to provide a wider range of applicable fields. This is accomplished by combining a specified ester-based compound, as a mold separating agent, into PAS resin.
2. Background of the Invention
In recent years, high heat-resistant thermoplastic resin has been in demand as a component material of instruments for electrical, electronic, automobile, and chemical applications. PAS resin may satisfy this need. However, PAS resin occasionally suffers a drawback in that stable and continuous molding becomes difficult, resulting in a slow molding speed (molding cycle) and poor productivity. This problem arises because PAS resin has good affinity with metals and shrinks slightly in the process of solidification from a molten state. On the other hand, many moldings require the use of precise and complicated metal molds, leading to poor mold separability.
In order to overcome these defects related to mold separability, some countermeasures have been taken in which the cavity of a metal mold is sprayed with silicone oil, or PAS resin is added with zinc stearate (Published Unexamined Japan Patent Application No. 54-162752) or fatty acid amide such as N,N'-alkylene bisalkane amide (U.S. Pat. No. 4,395,509).
For this purpose, however, silicone oil, when sprayed into the cavity, exhibits remarkable mold separability but must be sprayed once or more for every few shots. In the case of moldings having a weld part, the oil concentrates on the weld part and deteriorates weld strength, duplicating the problem with PAS resin. In addition, electrical contacts may malfunction because silicone oil attaches to moldings when the moldings are used for electric or electronic parts. Adding zinc stearate or fatty acid amide (such as N,N'-alkylene bisalkane amide) to some degree aids mold separation, but discoloration, lowering of the mechanical strength in moldings, and gas generation due to the low thermal decomposition temperature of the added compounds also result in kneading and molding processes. Generated gas also lowers resin strength at weld parts in moldings.